(a) Field of the Invention
The present invention relates to a thin film transistor substrate and its manufacturing method, and in particular, to a thin film transistor substrate having a stable thin film transistor characteristic and its manufacturing methods.
(b) Description of Related Art
A liquid crystal display (LCD) is one of the most widely used flat panel display types. An LCD includes two panels provided with field-generating electrodes such as pixel electrodes and a common electrode, and a liquid crystal (LC) layer interposed therebetween. The LCD displays images by applying voltages to the field-generating electrodes to generate an electric field in the LC layer, which determines orientations of LC molecules in the LC layer to adjust polarization of incident light.
A thin film transistor substrate includes a gate line and a data line crossing each other on a base substrate, and a switching element connected to a pixel electrode.
Switching elements, such as thin film transistors, are used to apply voltages to the pixel electrodes switching elements. When a gate on voltage is applied to gate electrodes of the transistors, the transistors are turned on and supply voltages for images to the pixel electrodes through source electrodes of the transistors. When a gate off voltage is applied to the gate electrodes, the transistors are turned off and the pixel electrodes maintain the applied voltages.
General processes for thin film transistor array substrate will be explained below.
A gate wire is formed on a base substrate made of material such as glass.
A first insulating layer formed on the gate pattern and the base substrate by depositing a first insulating material.
The semiconductor layer is formed on the first insulating layer by depositing a semiconductor material.
A second wire is formed on the semiconductor layer and the first insulating layer.
A second insulating layer is formed on the second wire, a semiconductor layer and the first insulating layer.
A pixel electrode is formed on the second insulating layer.
However, the semiconductor layer will be made of amorphous silicon, poly-silicon, or semiconductor.
A thin film transistor made of amorphous silicon can be fabricated cost-effectively with good uniformity, but has poor characteristic of mobility and stability.
In contrast, a thin film transistor made of poly-silicon has good characteristic of mobility and stability, but has poor characteristic of uniformity and needs relatively high production cost.
A thin film transistor made of semiconductor oxide has good characteristics of mobility and stability, and can be fabricated cost-effectively with good uniformity.
However, in the event of forming semiconductor layer made of semiconductor oxide, it is very difficult to use dry-etching for patterning, therefore wet-etching will be used for this patterning. This means that the semiconductor oxide layer can be easily etched or damaged by an etchant that will used in subsequent etching process and has a similar etching property to the etchant used in etch process for its own pattern.
During the aforementioned general processes for thin film transistor array substrate, the second wire is formed on the semiconductor layer. The patterning of the second wire is usually executed by wet-etching. Therefore, during the patterning of the second wire, the below semiconductor layer may be damaged by the wet-etching, which will give a bad effect on the characteristic of thin film transistor and display quality.